1. Field of the Invention
The invention relates to a method for digitally coding a composite signal which comprises a video signal and another signal.
2. Description of the Prior Art
A method for digitally coding a composite signal, formed of a video signal and another signal, is generally known. To digitally code or digitize an analog video signal, the video signal is converted into a digital signal by sampling the analog video signal and reproducing each sample obtained in this way using N bits (N-bit pulse code modulation, for example 8-bit PCM). If a composite signal which comprises a video signal situated in a base band and another signal situated outside the base band (such as, for example, a data signal) is to be digitize (the amplitude of the video signal is in this case generally ten to twenty times greater than the amplitude of the other signal), nothing in fact changes in the procedure mentioned and no additional problems arise. If, however, each sample of the analog composite signal is reproduced using fewer bits by reducing the number of bits in the case of N-bit PCM to a minimum of 1-bit PCM, in which case the spacings between the quantization levels increase after decoding, and by reducing the number of bits in the case of N-bit noise-shaped PCM to a minimum of 1 -bit noise-shaped PCM such as delta-sigma modulation, in which case the spacings between the quantization levels, which are not equidistant under these circumstances, also increase after decoding, which increased spacings can be reduced by increasing the oversample factor, additional problems arise in all cases because, after decoding, the video signal situated in the base band is found to disadvantageously affect the other signal situated outside the base band.